The invention relates generally to dynamic spine prostheses. In particular, the invention relates to dynamic spine prostheses with components whose position with respect to a spine fixation element may be adjusted.
There are multiple types of spine modification devices that may be implanted by attachment to one or more vertebrae to treat a variety of disorders. For example, spinal fusion systems fix the spatial relationships between two or more vertebrae. One such system is described in U.S. Pat. No. 6,080,156. Fusion systems, such as the one shown in the '156 patent, are typically attached to the vertebrae by screws placed in the pedicle. Because all components of such fusion systems are essentially immobile with respect to each other, each component must continually bear and transmit to adjacent components all forces exerted on the device anywhere in the device until the treated vertebral bodies have fused, at which point the bony fusion generally absorbs the majority of the intervertebral loads. Because such fusion devices are typically utilized in conjunction with other fusion-promoting techniques and tools, such as disc evacuation and packing with bone graft, the use of interbody fusion cages and bone graft, gutter grafting and/or the use of BMP or other arthrodesis promoting tools and techniques, it is generally only necessary for such fusion devices to function for a limited amount of time before the arthrodesis assumes the majority of the vertebral loading.
Unlike fusion systems, however, dynamic spine prostheses attach to two or more vertebrae and have components that move with respect to each other as the vertebrae to which they are attached move. Moreover, dynamic spine prostheses should be designed to assume normal physiological loading (as well as transient excessive loading conditions) for the lifetime of the patient, which could easily exceed 10,000,000 cycles or more. Dynamic spine prostheses can include artificial facet joint prostheses (such as, e.g., the Total Facet Arthroplasty System® available from Archus Orthopedics, Inc., the AFRS system available from Facet Solutions, and the TOPS system available from Impliant, Ltd.) as well as dynamic stabilization systems (such as, e.g., the Stabilimax NZ system available from Applied Spine Technologies, the Axient system available from Innovative Spinal Technologies, the N-Flex system available from N-Spine, and the Accuflex system available from Globus Medical.) and dynamic interspinous-spacer systems (such as, e.g., the X-Stop system available from Kyphon/St. Francis Medical Technologies, the Coflex system available from Paradigm Spine, the Extensure system available from Nuvasive, and the Wallis system available from Abbott Spine.).